1. Field of the Invention
The present invention relates to a vehicular room illuminating lamp capable of switching a mode between a mode in which a light source can be turned on/off irrespective of an open/close state of a door and a mode in which the light source can be turned on/off in response to the open/close state of the door.
2. Description of the Related Art
A conventional vehicular room illuminating lamp is disclosed in Japanese Patent Laid-Open Publication No. 2006-62640. As shown in FIG. 1, this vehicular room illuminating lamp 100 includes: a housing 102; a cover member 103; two illumination units 104 and 105; a mode switch 106; and a wire harness WH in a flat shape. The housing 102 and the cover member 103 are fixed to an indoor ceiling plate 101 by using an opening portion 101a thereof. The illumination units 104 and 105 are mounted into the housing 102. The mode switch 106 is mounted to an inside of the housing 102 and between the two illumination units 104 and 105. The wire harness WH passes through a space among the two illumination units 104 and 105 and the mode switch 106, the space serving as a cabling route.
The two illumination units 104 and 105 are arranged so that respective lamps L1 and L2 can individually irradiate seat positions in a vehicle cabin, which are close to two doors (not shown). The mode switch 106 engages with an operation knob 103a of the cover member 103. The mode switch 106 is adapted to be operable through the operation knob 103a. 
The respective illumination units 104 and 105 include switches SW1 and SW2, respectively, together with the lamps L1 and L2 as light sources. The respective switches SW1 and SW2 are protruded to the vehicle cabin side from respective holes 103b and 103b of the cover member 103. The respective switches SW1 and SW2 are adapted to be directly operable. The respective switches SW1 and SW2 are installed at positions where passengers on the seats close to the respective doors (not shown) are capable of operating the switches SW1 and SW2 with ease.
Next, a description will be made of a circuit configuration of the vehicular room illuminating lamp 100. As shown in FIG. 2, the wire harness WH is composed of a power supply wire B, a ground wire G, a courtesy wire C and a bypass wire P. The power supply wire B is connected to a battery, and the ground wire G is connected to the ground. The courtesy wire C is grounded through a door opening/closing switch unit (not shown). The door opening/closing switch unit is composed so as to ground the courtesy wire C when either one of the two doors is open, and otherwise, to set the courtesy wire C to an open state.
The mode switch 106 includes: two fixed contacts 106a and 106b; and a movable contact 106c that allows the fixed contacts 106a and 106b to conduct/nonconduct with each other. The two fixed contacts 106a and 106b are connected to the power supply wire B and the ground wire G, respectively. The mode switch 106 can switch a mode between a door mode in which the movable contact 106c allows the two fixed contacts 106a and 106b to conduct with each other and a light-off (OFF) mode in which the movable contact 106c allows the two fixed contacts 106a and 106b to nonconduct with each other.
The switch SW1 of the illumination unit 104 includes three fixed contacts 104a, 104b and 104c, and a movable contact 104d that selectively allows two of the fixed contacts to conduct/nonconduct with each other. The switch SW2 of the illumination unit 105 includes three fixed contacts 105a, 105b and 105c, and a movable contact 105d that selectively allows two of the fixed contacts to conduct/nonconduct with each other. The three fixed contacts 104a, 104b and 104c are connected to the ground wire G, the power supply wire B and the bypass wire P, respectively, and the three fixed contacts 105a, 105b and 105c are connected to the ground wire G, the power supply wire B and the bypass wire P, respectively. Switching can be made between a light-on (ON) mode in which the movable contacts 104d and 105d allow the first fixed contacts 104a and 105a and the second fixed contacts 105b and 105b to conduct with each other and the door mode in which the movable contacts 104d and 105d allow the second fixed contacts 104b and 105b and the third fixed contacts 104c and 105c to conduct with each other.
In the above-described configuration, when the ON mode is selected by either of the switches SW1 and SW2, the lamps L1 and L2 of the illumination units 104 and 105 concerned are turned on no matter which of the modes may be selected by the mode switch 106.
When the door mode is selected by the mode switch 106, and the door mode is selected by the two switches SW1 and SW2, the lamps L1 and L2 are turned on under a condition where the doors are open.
When the OFF mode is selected by the mode switch 106, even if the door mode is selected by the two switches SW1 and SW2, the lamps L1 and L2 are not turned on no matter whether or not the doors (not shown) are open.
As described above, in the vehicular room illuminating lamp 100, the respective passengers can select to turn on/off the lamps L1 and L2, and in addition, a driver and the like can select to turn on/off all the lamps L1 and L2 in a lump.